AEM Page Editor error : Handler of component is invalid -> TypeError: Cannot read property 'flow' of undefined

Hi All 

   To anyone who will face this issue in the future, please find below the details how this was fixed in my local. 

Root Cause : 

If you click on the last line where the error is occurring from the error trace , it will take you to a JS in the libs. Please check the below screenshots

Click on Pretty Print and it will highlight the error lines 

If you hover on the clientlibs it will give you the path of the clientlibrary , which is at /libs/cq/gui/components/authoring/editors/clientlibs/core  . I pulled the files under this path and did a search to find the JS which was causing issue and it took me to /libs/cq/gui/components/authoring/editors/clientlibs/core/js/util/util.js 

The error is happening at line number 254 of the file , where the argument code , passed to this method is actually passing as undefined.

To fix this , we can add an if condition as below

or you can replace the below line of code in your file from 254 - around 268 

ns.util.sanitizeCQHandler = function (code) {
    var handler;
    if(!code){
        try {
            handler = eval('(' + code + ')');
        } catch (ex) {
            handler = $.noop;
            $(document).trigger($.Event("error", {
                message: "Handler of component is invalid",
                exception: ex
            }));
        }
    }
    return handler;
};

This should ideally fix the issue. Hope this helps.

Thanks

Veena